Abstract—In the San Miguel de Allende basin, Guanajuato State, Mexico, two mandibles of gomphotheriids were collected, and by their diagnostic characters have been assigned to Stegomastodon primitivus. The jaws correspond to different ontogenetic and stratigraphic ages. In the Rancho El Ocote fauna, in the upper part of the Hemphillian stratigraphic sequence, the mandible of a young individual and isolated upper and lower molars were collected together with the mandible from the Blanco layer, which has been assigned a latest Hemphillian (Hh4) age. The molars have characters considered more primitive than those described for Stegomastodon primitivus (= Stegomastodon rexroadensis), characteristic of an early Blancan age in North American faunas. The jaw from the Blanco layer has a very short anterior symphysis, straight and ending in a narrow structure that forms the lingual canal. It has no evidence of tusks. The isolated molars present the most primitive characters referred to a Stegomastodon individual: The trefoil and entotrefoil cusps are simple without folds (ptychodonty) or accessory enamel tubercles (choerodont). The isolated M3/m3 has with four lophs/lophids and two large cusps posterior to the fourth lophs/lophids. The m2 has three lophids and two small conids behind the tritolophid, that, in advanced states of wear, form a posterior half lophid more evident in molars with greater wear. There are no stratigraphic indexes of a late Hemphillian or early Blancan age in the Blanco Layer. Throughout the Blanco Layer only Dinohippus mexicanus is present. Zircons separated from ash in the same layer where the Stegomastodon primitivus mandible was collected yielded a 4.85+0.17 Ma U-Pb age, which corresponds to the latest Hemphillian (Hh4). This Rancho El Ocote record is the oldest known among North American faunas. This result assumed that the possible diversification of gomphotheriids in faunas of central Mexico happened before that expected by Savage (1955) in his probable phyletic dispersal pattern of the North American gomphotheriids.
A mandible of an old adult gomphothere was collected in the Arroyo Earth Watch, in Los Galvanes area. The fossil was found in sediments assigned to the early Blancan. The jaw is complete without distortion, and it only retains the m3 in an advanced state of wear. This tooth only has five lophids that differentiate it from the m3s of Cuchillo Negro Creek and Elephant Butte Lake Stegomastodon of the early Blancan of New Mexico, that have 5+ to six lophids.
The zircons analyzed by the U / Pb method gave an age of 2.9±0.07 Ma for the Stegomastodon jaw from Los Galvanes, consistent with the early Blancan. This record correlates with specimens from New Mexico’s Cuchillo Negro Creek and Elephant Butte Lake faunas, that have a radiometric age of 3.1±0.3 Ma, early Blancan. The similarity of these radiometric ages suggests that Stegomastodon primitivus had a wide geographic distribution in the early Blancan.
more »
« less
Two species of gomphotheriids (Mammalia-Proboscidea) collected in early Blancan deposits of central Mexico, Rhynchotherium falconeri and the first record of Rhynchotherium browni outside of Sonora: A comparison
Abstract—This work describes and compares the skull and lower jaw of two species of Rhynchotherium discovered in early Blancan deposits in central Mexico. This comparison establishes the differences between the species Rhynchotherium falconeri and R. browni and is the first record of R. browni outside of San José de Pimas, Sonora. The description of the skull and jaw of the same individual, referred to the gomphotheriid proboscidean Rhynchotherium falconeri, collected in deposits of early Blancan age (3.6 Ma), from the Rancho La Goleta locality, state of Michoacán, Mexico, corresponds to an adult individual that shows these diagnostic characters: deflection of the symphysis down and forward with an angle of 61°, the anterior edge of the ascending ramus at 90°, and the ventral inclination of the horizontal ramus at 25°, which gives it greater depth characteristics in the anterior region under the protolophid of m2. These are characters that support referral to Rhynchotherium falconeri, however, M3/m3 are simple tetraloph/tetralophid, with low cusps and simple trefoils, without accessory cusps or a heel. The anteroposterior length of M3 is among the smallest of Rhynchotherium falconeri known in faunas of North America. These measurements are within the range considered part of sexual dimorphism, so the specimen is assumed to correspond to a female. The skull is domed, the occipital almost straight in relation to the occlusal surface of the molars, the face is more elongate, and the premaxillae are narrow and open, so they are separated in the anterior medial part, the alveoli are complete with apparent divergent direction, and two long fragments of tusks are separated from the alveoli with small evidence of enamel.
In the San Miguel de Allende basin, in deposits of early Blancan age (3 Ma) in the Los Galvanes area, the first known record of Rhynchotherium browni was collected outside of San José de Pimas, Sonora. The jaw is larger, and the structures are more robust. The symphysis, although reconstructed, shows a probable inclination of ~77°, and the anterior edge of the ascending rami has an angle of 107°. The mandible presents the alveoli of m1’s, and in front of them an extension of the lingual canal of approximately 70 mm. The horizontal ramus is longer and straighter, and shallower but wider transversely at the base of the ascending rami compared to Rhynchotherium falconeri. The M2 has three lophs, and the metaloph has a remarkable double trefoil. In m2 the tritolophid has a small cusp with signs of wear in the posterior medial part. The M3/m3 are tetraloph with simple trefoils and higher cusps, and have a heel represented by small cusps. The right i2 is complete, with no evidence of enamel.
more »
« less
- Award ID(s):
- 1949742
- NSF-PAR ID:
- 10339547
- Date Published:
- Journal Name:
- New Mexico Museum of Natural History and Science Bulletin
- Volume:
- 88
- Page Range / eLocation ID:
- 59-76
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)The lower jaw of the holotype of Adalatherium hui, from the Late Cretaceous of Madagascar, is the most complete yet known for a gondwanatherian mammal. It reveals for the first time the morphology of the character-rich ascending ramus of the dentary in a gondwanatherian. Each half of the lower jaw is composed of only one bone, the dentary, which is short and deep and houses only five teeth: an enlarged, procumbent incisor and four postcanine teeth. In comparable parts of its anatomy, the dentary of Adalatherium is strikingly similar to that of Sudamerica but differs slightly from that of Galulatherium (conformation anterior to first postcanine, mental foramen position), the only two other gondwanatherians represented by complete horizontal rami. Among other Mesozoic mammaliaform taxa, the dentary of Adalatherium is most similar to those of the largely Laurasian group Multituberculata, most notably in absence of postdentary trough and Meckelian sulcus; presence of short, deep dentary with sizable diastema and articulating with squamosal via mediolaterally narrow condyle that continues onto posterior surface (i.e., no distinct peduncle); possession of much reduced dentition; absence of angular process; possession of large pterygoid fossa and pterygoid shelf, ventral surface of which is flat; absence of coronoid bone; and possession of unfused mandibular symphysis. Most of these features are clearly derived and stand in stark contrast to the much more plesiomorphic morphology exhibited by the lower jaw of the haramiyaviid Haramiyavia. The lower jaws of euharamiyidans, although derived in their own right, are also relatively plesiomorphic.more » « less
-
more » « less
Abstract We report a new genus and species of herbivorous mammal,
Pahelia mysteriosa , from the early Eocene Cambay Shale Formation, Tadkeshwar Lignite Mine, Gujarat, India. The new taxon, approximately the size of a small phenacodontid (e.g.Ectocion parvus ), is represented by three mandibular fragments, the most complete of which documents nearly the entire symphysis and mandibular body plus P3–M3.Pahelia has incipiently selenolophodont molars with strong exodaenodonty, absent paraconids, weak but distinct entolophids, and prominent ectostylids. Molar size increases distally, but M3does not develop a prominent third lobe. Premolars are simple, with prominent protoconids and short talonids but little development of other trigonid cusps. The mandibular symphysis is strongly fused, and there is an enlarged alveolus for an anterior tooth. The combination of features present in the new taxon does not closely match that of any known mammal, but there are some similarities to a diversity of ungulates from Africa, Asia, Europe and North America. Preserved morphology is insufficient to assess the affinities of the new taxon with confidence, but a link to Quettacyonidae, also endemic to the Indian subcontinent, is morphologically and biogeographically plausible. If this scenario is correct, it suggests thatP. mysteriosa could be a part of the endemic mammalian fauna of India prior to its initial faunal contact with Asia. -
Abstract The Placerias /Downs’ Quarry complex in eastern Arizona, USA, is the most diverse Upper Triassic vertebrate locality known. We report a new short-faced archosauriform, Syntomiprosopus sucherorum gen. et sp. nov., represented by four incomplete mandibles, that expands that diversity with a morphology unique among Late Triassic archosauriforms. The most distinctive feature of Syntomiprosopus gen. nov. is its anteroposteriorly short, robust mandible with 3–4 anterior, a larger caniniform, and 1–3 “postcanine” alveoli. The size and shape of the alveoli and the preserved tips of replacement teeth preclude assignment to any taxon known only from teeth. Additional autapomorphies of S. sucherorum gen. et sp. nov. include a large fossa associated with the mandibular fenestra, an interdigitating suture of the surangular with the dentary, fine texture ornamenting the medial surface of the splenial, and a surangular ridge that completes a 90° arc. The external surfaces of the mandibles bear shallow, densely packed, irregular, fine pits and narrow, arcuate grooves. This combination of character states allows an archosauriform assignment; however, an associated and similarly sized braincase indicates that Syntomiprosopus n. gen. may represent previously unsampled disparity in early-diverging crocodylomorphs. The Placerias Quarry is Adamanian (Norian, maximum depositional age ~219 Ma), and this specimen appears to be an early example of shortening of the skull, which occurs later in diverse archosaur lineages, including the Late Cretaceous crocodyliform Simosuchus . This is another case where Triassic archosauriforms occupied morphospace converged upon by other archosaurs later in the Mesozoic and further demonstrates that even well-sampled localities can yield new taxa.more » « less
-
Archaic human remains from Hualongdong, China, and Middle Pleistocene human continuity and variationMiddle to Late Pleistocene human evolution in East Asia has remained controversial regarding the extent of morphological continuity through archaic humans and to modern humans. Newly found ∼300,000-y-old human remains from Hualongdong (HLD), China, including a largely complete skull (HLD 6), share East Asian Middle Pleistocene (MPl) human traits of a low vault with a frontal keel (but no parietal sagittal keel or angular torus), a low and wide nasal aperture, a pronounced supraorbital torus (especially medially), a nonlevel nasal floor, and small or absent third molars. It lacks a malar incisure but has a large superior medial pterygoid tubercle. HLD 6 also exhibits a relatively flat superior face, a more vertical mandibular symphysis, a pronounced mental trigone, and simple occlusal morphology, foreshadowing modern human morphology. The HLD human fossils thus variably resemble other later MPl East Asian remains, but add to the overall variation in the sample. Their configurations, with those of other Middle and early Late Pleistocene East Asian remains, support archaic human regional continuity and provide a background to the subsequent archaic-to-modern human transition in the region.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- The DOI is not currently available.
